1. Field of the Invention
The present invention relates to tool changers and, in particular, to a tool changer of a machine tool that performs tool indexing by turning of a turret.
2. Description of the Related Art
A tool changer that automatically changes a tool which is attached to a main axis of a machine tool has been used. In this tool changer, a plurality of tools necessary for work are set in advance, and the tool changer is configured so as to automatically change a tool which is attached to the main axis of the machine tool to a designated tool in accordance with the process of machining.
In a machine tool provided with the existing tool changer, a controller of the machine tool generally recognizes only the position or phase of a turret drive source and does not directly recognize the actual position of a turret. As a result, if a difference is caused between the turret phase which is recognized by the controller of the machine tool and the actual turret phase, tool change cannot be performed normally. This makes it necessary for work to eliminate the difference.
In order to solve the above problem, the technique disclosed in Japanese Patent Application Laid-Open No. 2015-139842 implements a machine tool having the function of automatically conducting work which eliminates the difference by detecting variations in a load which periodically occur by turning of a turret and setting a reference phase for turret indexing based on the detection result.
However, the method disclosed in Japanese Patent Application Laid-Open No. 2015-139842 has a problem of false detection of a reference phase, that is, if the positions in which load variations, which periodically occur at the time of turning of the turret, occur change by an entry of a foreign substance into a mechanism portion which performs turret indexing, a reference phase is set based on the changed load variations. Moreover, the method also has a problem of the difficulty of detecting a reference phase if load variations, which periodically occur at the time of turning of the turret, become smaller by the occurrence of wear in a turret mechanism part.